1. Field of the Invention
The present invention relates to a diagnosis device for an internal combustion engine and a diagnosis method thereof.
2. Description of Related Art
As disclosed in Japanese Patent Application Publication No. 2005-61335 (JP 2005-61335 A), air flow meter diagnosis processing may be executed when the vehicle is being decelerated with fuel cut off. In the air flow meter diagnosis processing, when the intake air amount that is detected by an air flow meter is out of a predetermined normal range, the duration of the state is measured. When the duration is longer than a threshold value, the air flow meter is diagnosed as not normal.
In Japanese Patent Application Publication No. 2007-85225 (JP 2007-85225 A), one example of EGR diagnosis processing is described. In Japanese Patent Application Publication No. 2007-85225 (JP 2007-85225 A), an EGR valve that is provided in a return passage through which a portion of exhaust gas is returned into an intake pipe as EGR gas. In the EGR diagnosis processing, the EGR valve is forcibly opened and closed when the vehicle is being decelerated and the fluctuation of intake pressure in the intake pipe at this time is detected. Based on the result of comparison between the extent of the detected fluctuation of intake pressure and a predetermined failure determination value, the EGR device is diagnosed as being able to operate normally or not.
The intake pressure in the intake pipe can be calculated based on the intake air amount that is detected by an air flow meter. Thus, when both air flow meter diagnosis processing and EGR diagnosis processing are executed, it is desirable that the air flow meter diagnosis processing is executed first and the EGR diagnosis processing is executed after the air flow meter has been confirmed to be normal to ensure reliability of the EGR diagnosis processing.